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Early experience in brain tumor localization at this institution, utilizing diiodofluorescein I 131 and scintillation counter "spot checking," proved this technique suitable only for screening. 1,2 Further progress elsewhere included development of scanning scintillation detectors, 3 photographic recording, 4,5 and more suitable scanning agents including radiomercury-labeled chlormerodrin (Neohydrin). 6 Our present program utilizing the above refinements in equipment and radiomercury-tagged chlormerodrin has proved useful in the localization of intracranial tumors in the majority of cases prior to contrast studies. The isotope initially used was Hg 203 tagged to chlormerodrin. This compound was introduced in 1959 as an agent for brain scanning by Blau and Bender 6 who found it significantly better than albumin I 131.7 Hg 203 decays with a half life of 45.8 days with the emission of a low energy β-particle to an excited state of Tl 203 , which in turn emits a single 0.28 mev γ-ray.

Radioisotope scanning techniques are now accepted as a valuable adjunct to classical contrast studies in the localization of intracranial tumors. However, advocates of these methods have not approached supratentorial and subtentorial tumors with equal enthusiasm, the latter being regarded as less amenable to localization by scintiscan techniques. Sweet et al 1 utilizing positron emitters characterized their results with posterior fossatumors as "miserable" (59% missed), and McAfee, 2 utilizing radioiodinated human serum albumin and scintiscan techniques, obtained "poor" (four of six missed) results with this type of tumor. Early experience here in localization of posterior fossa tumors utilizing scintillation probe multispot survey over the head after administration of I 131 diiodofluorescein was disappointing in that correct localization was suggested in only three of 11 cases. 3 More recently we began a program ultilizing further refinements of technique (scanning scintillation detector, effective collimation, and photographic recording) and radiomercury-labeled chlormerodrin. Eighty-four per